Those old monojet's that came stock will suck some gas. Economy wasn't a concern back then. There are plenty of carburetors that will yield better mileage, but finding the proper intake might be more of a problem. There are many 4bbl, and multiple carb manifolds available, but I don't know of any that would accept a 2bbl. I use one of these
Holley 390 cfm 4bbl, and get very good mileage from a 305. It's the same four barrel that they spec for 6 bangers.